This invention relates in general to magnetic tape record/reproduce apparatus and, more particularly, this invention relates to a helical scan magnetic tape record/reproduce apparatus having a rotary head scanner which includes a reflective tachometer/headwheel assembly.
Advanced magnetic tape recording and reproducing systems are required to store ever larger quantities of analog and digital information in ever smaller areas. In helical scan recording/reproducing equipment, a rotary head scanner having one or more magnetic heads records and reproduces inFormation in slant tracks on magnetic tape. Typically, a plurality oF magnetic record and reproduce heads are mounted on the periphery of a headwheel which rotates between upper and lower stationary drums. In order to accurately and reliably record and reproduce inFormation from magnetic tape, it is desirable that the rotational speed of the magnetic heads be kept constant. It is also desirable that a magnetic head properly track a recorded track on the tape so that an optimal signal is reproduced.
Servo systems which effect constant rotational speed of the headwheel of a rotary head scanner, utilize a separate tachometer which is mounted on the headwheel shaft at a distance from the headwheel. The tachometer may comprise a magnetic disk which is sensed by a magnetic pick-up head (see for example, U.S. Pat. No. 3,402,257, issued Sept. 17, 1968, entitled MAGNETIC RECORDING OF TELEVISION SIGNALS WITH PRERECORDED SYNC SIGNALS). The tachometer may also include an optically transparent disk having a light source and light sensor located on oPposite sides of the disk to sense circumferential marks on the disk (see U.S. Pat. No. 3,600,508, issued Aug. 17, 1971, entitled VIDEO TAPE RECORDER WITH EDITING FEATURE AND lMPROVED TAPE SPEED CONTROL). Although separate tachometer disks may be useful for the purposes for which they are intended, they disadvantageous in applications where sPace is at a premium. Thus, the separate disk and sensor assemblies take up space which increases the size of the rotary head assembly. It has also been ProPosed to incorporate into the headwheel carrying rotating magnetic heads, a transmission type tachometer disk. Such a device is disclosed in U.S. Pat. No. 4,319,294 issued Mar. 9, 1982, entitled MAGNETIC TAPE SCANNING DEVICE FOR RECORDING AND/OR REPRODUCING BAND SIGNALS. Although this device eliminates the necessity for a separate tachometer, such a design is disadvantageous, because separate assemblies must be provided on each side of the disk to support light sources and light sensors. Moreover, as shown in FiG. 3B of the latter patent, the conductors which extend from the magnetic heads mounted on the periphery of the disk tend to interfere with the tachometer markings and 25 may give a false indication of the rotational speed of the headwheel.